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6

A STUDY OF MECHANICAL PROPERTIES AND CRUSHING

PERFORMANCE OF CARBON FIBER WOUND TO HDPE PIPE (CFWHP)

BHUVANA RUEBEN A/L AIYYAPPAN

MECHANICAL ENGINEERING

UNIVERSITI TEKNOLOGI PETRONAS

JANUARY 2016


PERFORMANCE OF CARBON FIBER WOUND TO HDPE

PIPE (CFWHP)

by


15986

Dissertation submitted in partial fulfilment of the requirements for the

Bachelor of Engineering (Hons)

(Mechanical Engineering)

FYP II JANUARY 2015

Universiti Teknologi PETRONAS

32610, Bandar Seri Iskandar

Perak Darul Ridzuan

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i

CERTIFICATION OF APPROVAL


PERFORMANCE OF CARBON FIBER WOUND TO HDPE PIPE (CFWHP)

by


15986

A project dissertation submitted to the

Mechanical Engineering Programme

Universiti Teknologi PETRONAS

in partial fulfillment of the requirement for the

BACHELOR OF ENGINEERING (Hons) (Mechanical)

Approved by,

________________________

(AP IR DR HAMDAN HAJI YA)

UNIVERSITI TEKNOLOGI PETRONAS

TRONOH, PERAK

JAN 2016

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ii

CERTIFICATION OF ORIGINALITY

This is to certify that I am responsible for the work submitted in this project,

that the

original work is my own except as specified in the references and

acknowledgements,

and that the original work contained herein have not been undertaken or done

by

unspecified sources or people.

_________________________

(BHUVANA RUEBEN A/L AIYYAPPAN)

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iii

ABSTRACT

Carbon fiber-reinforced polymer, is a type of composite polymer which is highly

regarded as one of the best alternatives for light weight, strong and anti-corrosion

material. Composite polymer consists of 2 main constituent materials which are

matrix and reinforcement which are fabricated using the filament winding technique.

This material is vastly used in various industries such as the automotive industry, oil

and gas industry, aerospace industries and also industries that demands a high

strength-to- weight ratio criteria. The focal point of this research is to study the effect

of different carbon fiber tow arrangements on the carbon fiber tow wind to HDPE

composite pipe (CFWHP) and their mechanical properties. There are 3 types of

samples used in this project, both with different carbon fiber tow arrangements.

These samples will be then fabricated in SIRIM Permatang Pauh using epoxy resin

as the desired matrix to form the composite material. The first sample with an

arrangement of 4 fiber tows of 12k carbon fiber (total of 48k) with a winding angle

of 57°. Followed by the second arrangement of 2 fiber tows of 12k carbon fiber and

4 fiber tows of 6k carbon fiber (total of 48k). Lastly, the third and final arrangement

of 8 fiber tows of 6k carbon fiber (total of 48k). Consequently, tensile test and

compression test will be done to get an idea on how the mechanical properties of

CFWHP will be affected by the different carbon fiber tow arrangements.

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iv

ACKNOWLEDGEMENT

I would like to express my deepest gratitude to my supervisor, AP Ir Dr Hamdan

Haji Ya for providing me this great opportunity to embark on this project under his

supervision. I sincerely appreciate all the guidance which has been offered by AP Ir

Dr Hamdan Haji Ya along the way of completing this project. I had able to gain more

knowledge on the project through all the experiences shared by AP Ir Dr Hamdan

Haji Ya. Next, I would like to thank my co-supervisor Dr. Zaki Abdullah and all the

technicians in UTP as well as in SIRIM Permatang Pauh which lend their helpful

hand by the time I needed their help and guidance, especially the fabrication and

testing process. No doubt that my project had able to flow smoothly with the helps

that they had offered. Last but not least, I wish to thank my beloved family for their

never ending support that helps me push through to complete this project. Thank you.

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v

TABLE OF CONTENT

CERTIFICATION OF APPROVAL……………………………………………...i

CERTIFICATION OF ORIGINALITY………………………………………….ii

ABSTRACT………………………………………………………………………..iii

ACKNOWLEDGEMENT………………………………………………………...iv

CHAPTER 1: INTRODUCTION………………………….………………1

1.1 Background of Study……………………………… 1-2

1.2 Problem Statement…………………………….……. 3

1.3 Objectives………………………………….………...4

1.4 Scope of Study…………………………………….…4

1.5 Relevancy and Feasibility of Project…………….......4-5

CHAPTER 2: LITERATURE REVIEW…………………………………..6

2.1 Composite Material……………………………….…6-7

2.2 Carbon Fiber as Reinforcement……………………....8

2.3 Epoxy Resin as Matrix………………………………..9

2.4 High Density Polyethylene (HDPE)….........................10

2.5 Filament Winding Technique…………………….…11-12

2.6 Tensile Test……………………………………….. 13-14

2.7 Compression Test.......................................................15-16

2.8 Microstructure Test………………………………...... 17

2.9 CRFP in Oil & Gas Application………………….......18

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CHAPTER 3: METHODOLOGY…………………………………….…….19

3.1 Research Methodology………………………………..19

3.2 Process Flow Chart……………………………………20

3.3 Fabrication of CFWHP …………………………....21-22

3.4 Microstructure Test…………………………….……....23

3.3.1 Sample Preparation……………………….…... 24

3.3.1.1 Sectioning & Cutting………………………... 24-25

3.3.1.2 Grinding & Polishing…………………….…. 26-27

3.3.1.3 Microstructure Test Procedure ………….….. 28-29

3.5 Tensile Test (ASTM D638)………………………..... 30-31

3.6 Compression Test (ASTM D695).................................. 32

3.7 Gantt Chart & Key Milestone……………………….. 33-34

CHAPTER 4: RESULTS & DISCUSSION.....................................................35

4.1 Microstructure Test Analysis (Surface Section)…... 35-40

4.2 Microstructure Test Analysis (Cross Section)………...…41-46

4.3 Tensile Test (ASTM D638)……………………………...47-52

4.4 Compression Test (ASTM D695)………………………..53-58

CHAPTER 5: CONCLUSION & RECOMMENDATIONS………………...59

5.1 Conclusion……………………………………………….59-60

5.2 Recommendation………………………………………......60

REFERENCES……………………………………………………………………… 61-63

APPENDIX ……………………………………………………………………..……64-70

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LIST OF FIGURES

FIGURE 2.1: Body Diagram of Axial and Hoop Forces and Internal Pressure…12

FIGURE 2.2: AI-7000 M Universal Testing Machine…………………………..12

FIGURE 2.3: Universal Tensile Machine for Compression Test……………….15

FIGURE 2.4: Peak Loads of Past Research Sample……………………………16

FIGURE 2.5: Scanning Electron Microscope (SEM)…………………………..17

FIGURE 3.1: Project Process Flow Chart………………………………………20

FIGURE 3.2: Liner for Winding………………………………………………..21

FIGURE 3.3: Resin Bath………………………………………………………..21

FIGURE 3.4: The Fibers Wounding the Mandrel………………………………22

FIGURE 3.5: Scanning Electron Microscope (SEM)…………………………..23

FIGURE 3.6: The Cutting Area of the CFRP…………………………….…….24

FIGURE 3.7: Samples before Cutting………………………………………….25

FIGURE 3.8: Samples after Cutting……………………………………………25

FIGURE 3.9: Metaserv 250…………………………………………………….26

FIGURE 3.10: Placing of SiC Paper……………………………………………26

FIGURE 3.11: Grinding of the Specimen………………………………………27

FIGURE 3.12: Polishing of the Specimen……………………………………...27

FIGURE 3.13: Placement of the Sample in the Holder…………...………….....28

FIGURE 3.14: Adjustment of the Holder Height……………………………….28

FIGURE 3.15: Placement of the Holder in the Phenom……………………..….29

FIGURE 3.16: Observation of the Microstructure………………………………29

FIGURE 3.17: AI-7000 M Universal Testing Machine…………………………30

FIGURE 3.18: Dog-Bone Specimen Shape for Tensile Test (ASTM D695)…...31

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viii

FIGURE 3.19: CFWHP Pipe Specimen in Axial Position Compression Test.....32

FIGURE 4.1: Surface Section Point of Interest………………………………….35

FIGURE 4.2: 12k Fiber Tow Sample Arrangement……………………………..36

FIGURE 4.3: 12k + 6k Fiber Tow Sample Arrangement……………………..…36

FIGURE 4.4: 6k Fiber Tow Sample Arrangement……………………………...36

FIGURE 4.5: Comparison of Void Areas (Surface Section)

using Different Fiber Tow Arrangements………………………..37

FIGURE 4.6: Surface Void Formation for Sample A1………………………….38

FIGURE 4.7: Surface Void Formation for Sample B1……………………….....39

FIGURE 4.8: Surface Void Formation for Sample C1………………………….40

FIGURE 4.9: Cross Section Point of Interest…………………………………...42

FIGURE 4.10: Comparison of Void Areas (Cross Section)

using Different Fiber Tow Arrangements……………………...…43

FIGURE 4.11: Cross Section Void Formation for Sample A1…………………...44

FIGURE 4.12: Cross Section Void Formation for Sample B2……………………45

FIGURE 4.13: Cross Section Void Formation for Sample C2…………………...46

FIGURE 4.14: Comparison of Tensile Test Stress Loads

using Different Fiber Tow Arrangements……………………......48

FIGURE 4.15: Stress-Strain Curve for Sample A (12k)………………………….49

FIGURE 4.16: Stress-Strain Curve for Sample B (12k + 6k)………………...….50

FIGURE 4.17: Stress-Strain Curve for Sample C (6k)………………………...…51

FIGURE 4.18: Samples A (12k) after Tensile Test……………………………….52

FIGURE 4.19: Samples B (12k + 6k) after Tensile Test…………………………..52

FIGURE 4.20: Samples C (6k) after Tensile Test…………………………………52

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FIGURE 4.21: Compression Test Load-Displacement Curve……………………55

FIGURE 4.22: Side View of Samples A after Compression Test…………………56

FIGURE 4.23: Top View of Samples A after Compression Test…………………56

FIGURE 4.24: Side View of Samples B after Compression Test………………...57

FIGURE 4.25: Top View of Samples B after Compression Test…………………57

FIGURE 4.26: Side View of Samples C after Compression Test…………………58

FIGURE 4.27: Top View of Samples C after Compression Test………………….58

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LIST OF TABLES

TABLE 3.1: Technical Specifications of Scanning Electron Microscope (SEM)...23

TABLE 3.2: Technical Specifications of Universal Testing Machine…..………..30

TABLE 4.1: Calculations for 12k samples……………………………...………...35

TABLE 4.2: Calculations for 12k samples………………………….………...…..41

TABLE 4.3: Calculations for 12k sample…………………………….……………41

TABLE 4.4: Calculations for 6k samples………………………………...………..42

TABLE 4.5: Tensile Test Result Tabulation………………………………...……50

TABLE 4.6 : Compression Test Result Tabulation…………...………………...…56

1

CHAPTER 1

INTRODUCTION

1.1 Background

The world has now become a platform that is in need for engineering work that will

coincide with the huge demands of leading industries such as the automotive industry

and also the oil and gas industry due to the increasing human population. With that said,

the plea for more high performance materials such as the carbon fiber reinforced

polymers (CFRP) are increasing as we speak. This project is primarily aimed at the oil

and gas industry since the existing steel pipelines are only able to provide limited

benefits and are also subjects to corrosion. Due to this fact, the industry is now shifting

their attention towards nonmetallic pipelines. According to the Saudi Aramco News,

nonmetallic pipes are designed to last for 25 years in the field, which is a significant

improvement in piping lifespan compared to the conventional metallic pipes [1].

CFRP is a type of composite material where it is made out from carbon fiber and also

epoxy resin. Due to the usage of carbon fiber, the manufacturing cost of CFRP falls

more on the higher side. Despite the high cost, CFRP are also broadly used in the

aerospace industry for the manufacturing of ailerons, gear doors and engine nacelles.

Besides that, CFRP are extensively used in the making of exotic cars where high

strength-to-weight ratio is needed to manufacture the high performance vehicles.

Moreover, CFRP are now slowly making their climb up the oil and gas industry as it has

the capability to withstand the harsh subsea environment. All in all, the performance and

the durability provided by the CFRP clearly makes up for the high manufacturing cost

on the long run. However, there are also ways to also reduce the cost competitiveness

with new technological manufacturing techniques.

2

In order to reduce the manufacturing cost of the CFRP, a technique called filament

winding is used to wind the carbon fiber onto the high density polyethylene pipe

(HDPE). This technique has been identified as the most efficient and least costly way to

manufacture composite materials [2]. The primary interest of this project lies in the

relationship between various sizes of carbon fiber tow arrangements being wind onto the

HDPE pipe and how it affects the mechanical properties. However, the mechanical

properties of the carbon fiber wind to HDPE pipe (CFWHP) are highly dependent on the

proportions of carbon fiber and epoxy resin, orientation of carbon fiber, types of epoxy

resin, and size of carbon fiber and length of carbon fiber for discontinuous carbon fiber

and void content [3].

Throughout this project, the winding angle, winding tension, resin content, and

winding layer will be kept constant. The only manipulated variable in the project will be

the usage of various sizes of carbon fiber tow arrangements. Theoretically, by utilizing

similar sizes of fiber tow, small triangles or voids will be formed at every crossing part

which will then affect the properties of the CFWHP. In order to enhance the mechanical

properties of the CFWHP, the voids could be reduced by introducing the different sizes

of fiber tow arrangement but maintaining the same number of filaments in the sample.

Several tests such as tensile test and compression test will be done to study on how the

different types of carbon fiber tow arrangements affects the mechanical properties of the

CFWHP. At the end of the research, the results will be then tabulated to conclude on the

main objectives of this study.

3

1.2 Problem Statement

In the oil and gas field, it is roughly estimated that around 1.4 billion US dollars is

expended annually due to corrosion in the pipelines that are made out from metallic

pipelines. At the event of any leaking, 50% of the time, it is caused by corrosion [4].

How do we avoid this from occurring? For this research, the primary point lies in the

arrangement of the carbon fiber tow. There are 2 types of fiber tow bundles that will be

used. One being the 6k fiber tow, followed by the 12k fiber tow. These 2 samples are the

ones that are most commonly used in the market. The reason why we manipulate the

carbon fiber tow arrangements is to investigate on the formation of voids.

Voids will be formed due to small gaps at every crossing part when the fiber is being

wound around the mandrel [5]. These voids will then affect the mechanical properties of

the carbon fiber wind to HDPE pipe (CFWHP). So in order for us to find out the impact

that these voids have on the mechanical properties, a few tests must be done, such as the

compression test and tensile test. This will then prove crucial for us to understand on

which type of carbon fiber tow arrangement gives out the best mechanical properties.

4

1.3 Objective

The objectives of this project:

i. To study how various sizes of carbon fiber tow arrangements affect the level of

enhancement of mechanical properties the carbon fiber wind to HDPE pipe

(CFWHP)

ii. To analyze and discuss the findings obtained from the microstructure test, tensile

test and compression test respectively.

1.4 Scope of study

The scope of study of this project:

i. Conclude and study the results obtained from the tensile test, and compression

test on the carbon fiber wind to HDPE pipe (CFWHP)

ii. Take on the issue of the formation of voids in the CFWHP in order to enhance its

mechanical properties

5

1.5 Relevancy And Feasibility Of Project

The project is seen as important as it is looking into new possibilities of funding

alternative measures for pipelines in the oil and gas industry. The reason behind this

project is because of the high tendency of the commercial steel pipeline being subject to

corrosion. With the usage of carbon fiber reinforced polymer (CFRP), corrosion in

pipelines can be neglected as this composure material is corrosion resistant. Although it

is expensive, it will help oil companies save money in the long run by reducing

maintenance and downtime due to corrosion. Consequently, this project is very much

relevant as the subject matter is not widely studied into maximum potential. The project

is feasible since it is dealing with a specified scope of experiment. In this experiment,

the effect of different carbon fiber tow arrangements on the mechanical properties of

carbon fiber wound to HDPE pipe (CFWHP) will be studied. It is within capability of

the student to conduct the study with the guidance from the supervisor. It is positive that

this project can be conducted and accomplished with the given period.

6

CHAPTER 2

LITERATURE REVIEW

2.1 Composite Material

A composite material is created by bringing together two or more materials of

different properties. The combination of these various properties usually produces an

end product that is higher in quality and possess distinctive properties. Composite

materials come into play most of the time in our lives. For example, it is used in the

making of sporting equipment, body armor, aircraft parts and water pipes. The materials

that make up the composite material are called constituent materials [6]. There are two

primary types of constituent materials involved, mainly the reinforcement and matrix.

Both of these materials play their own pivotal roles in creating a proper composite

material. The reinforcement in this case acts as the material that gives the end product its

mechanical and physical properties. On the other hand, the matrix plays a supportive

role that maintains the positions of the reinforcement material or particles in place [7].

When compared to the commercial materials, composite materials tend to have the upper

hand in many aspects. One of them is that composite materials that it is lightweight and

easy to transport. This property will then contribute accordingly, depending on which

field that the composite material is being subject to. Looking at the automotive industry,

lightweight equates to more fuel savings. Then, in the energy industry, fan blades which

weigh lesser possess the ability to produce more energy as it requires less force for the

wind to rotate the blades. Hence, more power is being produced by the turbines [8].

7

As said earlier the main application of the project is aimed towards the oil and gas

industry. Composite materials are now beginning to be the attention grabbers when

compared to the more commercialized pipelines that are made out of metal. The

advantages provided by the pipelines that are made out from composite materials are in

abundance. The crucial one is that the composite materials possess non-corrosive

properties. Furthermore, composite materials also require low maintenance and are long

lasting [8]. Composite stiffness can be predicted using a micro-mechanics approach

termed the rule of mixtures. Where the rule of mixtures’ equation is as below in

Equation 1:

EC = EF VF + EMVM = EF VF + EM (1-VF) (1)

Where: EC = tensile strength of the composite

EF = tensile strength of the fiber

EM = tensile strength of the matrix

VF= volume fractions of the fiber

VM= volume fractions of the matrix

8

2.2 Carbon Fiber as Reinforcement

Carbon fiber is a type of material that comprises of fibers enclosing carbon atoms that

are aligned together to form a long axis. Carbon fiber is a super strong material which is

also lightweight at the same time. It is widely preferred as it is almost five times the

strength of steel. The other properties of carbon fiber include high stiffness, high

strength, lightweight, high chemical resistance and high temperature tolerance [9].

Actually, glass fibers are the more common fiber compared to carbon fibers but due to

the difference in strength, carbon fibers are highly preferred commercial wise. These

properties will prove to be a huge advantage when the application of the carbon fiber is

targeted towards the oil and gas industry, which is the main application of this research.

In the formation of carbon fiber reinforced polymer (CFRP), the carbon fiber acts as one

of the two constituent materials involved in the composite material formation process.

The two constituent materials being the reinforcement and matrix materials.

In this case, the carbon fiber acts as the reinforcement material. The role of the

reinforcement material is to display the mechanical and physical properties of the

desired composite material. With that said, the reinforcement material frequently possess

high tensile and compressive strengths. However, these cannot be achieved in the

structural form as there might be impurities present or other flaws during the processing

period. This flaws will then subsequently lead to formation of cracks. Hence, the

strength of the composite material will be affected [10]. However, when combined with

a matrix material of higher density, the reinforcement also aids to reduce the density of

the composite material, thus enhancing the mechanical properties of the composite

material such as specific strength [11].

9

2.3 Epoxy Resin as Matrix

In today’s modern day manufacturing field, there are a total of three types of resins

used to bind carbon fibers together onto polymers. They are epoxy resin, vinyl ester and

polyester resins respectively. The reason why that epoxy has been chosen as the desired

resin is because it is the strongest among the three resin types. To be precise, it is

roughly three times stronger than vinyl ester and polyester resins. Epoxy resins are

vastly used in the aerospace industry, automotive industry and also the marine industry.

They are mainly used as adhesives and also structural matrix [12]. However, among all

the resin types, epoxy resin is the most expensive but it is worth every penny. Besides

that, when combined with carbon fiber to form a composite material, the epoxy resin

stands out and it also form a practically leak-proof barrier [13]. One of the setbacks is

that the curing time for the epoxy is lengthier compared to vinyl ester and polyester

resins. Curing occurs at any temperature from 5°C to 150°C, however, their prolonged

range of properties can make epoxy resin the performance choice for critical

applications [14]. These are the reasons why the epoxy resin has been designated as the

desired resin in this project.

The matrix plays a crucial role in the forming of any composite material. The main

function of the matrix is to bind and support the reinforcement material by making sure

the position of the material is always maintained. Usually, the composite materials are

categorized based on the matrix material. For instance, it can be either polymer, metallic

or even ceramic. Not only that, the matrix does not only serve as a holder for the

reinforcement material, but it is also acts as a barrier to protect the reinforcement

material from harm either triggered by corrosion or high temperatures. On top of that,

the matrix also aids in spreading the load evenly to each individual reinforcement

material. As said earlier, there might be certain flaws during the processing period of the

reinforcement material which will then lead to the emerging of cracks. Through

technological developments, it has been uncovered that this issue can be solved by

combining the reinforcement material with a matrix material so that there is more

stability involved during the formation of the composite material [5].

10

2.4 High Density Polyethylene (HDPE)

High density polyethylene (HDPE) is a type of petroleum made thermoplastic. Today

HDPE has become one of the most used thermoplastics for production of plastic items,

utensils, films and pipes. HDPE is readied from ethylene by a catalytic process. The

nonattendance of branching results in an all the more firmly stuffed structure with higher

density and to some degree higher chemical resistance compared to Low Density

Polyethylene (LDPE). Other than that, HDPE also possess higher specific and tensile

strengths. They are also capable of withstanding temperatures ranging up to 120°C [15].

Our project will be focused on to the HDPE pipes that is used in the oil and gas industry

to transfer oil at high pressures and speeds. It is known for a fact that the lifespan of the

HDPE pipes can be over 50 years which is astonishing contrasted with its predecessor,

the carbon steel pipes, which can last up to around 20 years in the field.

The application of HDPE in the oil and gas industry may prove to bring a number of

benefits to the users. One of the main benefits is that the HDPE pipes are resistant to

corrosion and they do not undergo rusting as well. Furthermore, the pipes are also leak

tight or leak proof. The heat fused joints create a far stronger bond compared to the

HDPE pipe itself. Other than that, the flow rates are also known to be kept at optimum

rates. Since polyethylene is smoother than steel, cast iron, ductile iron, or concrete,

HDPE pipe that is smaller in size has the ability to convey an identical volumetric flow

rate at the same pressure Other than that, it has less drag and a lower chance for

turbulence at high flow. In addition to aid the installation process, HDPE pipes are

lightweight and they require light equipment for handling them. This will also come in

handy when it comes to the installation costs. HDPE permits bending without the

requirement for an excessive number of fittings. Since HDPE is not a fragile material, it

can be introduced with bends around uneven territory effortlessly in constant lengths

without extra welds [16].

11

2.5 Filament Winding Technique

Filament winding technique is a type of process that is focused on the manufacturing

of open or closed end parts. The working procedure includes winding fibers over a

mandrel under tension, in the case of the project, the mandrel would be the HDPE pipe.

The mandrel rotates while a wind eye on a carriage moves on a level plane, putting

down fibers as indicated by the designated pattern. The most common fibers used would

be glass fibers and carbon fibers. Carbon fibers would be the chosen fibers in this project

and would be coated with epoxy resin as they are wounded onto the HDPE pipe. Once

the mandrel has been secured totally as per the thickness wished, the mandrel is put in an

oven to cure and solidify the resin. The mandrel is then taken out, hence delivering the

hollow end component.

When the filament winding process is being conducted, there are a few parameters that

have to be manipulated, which are the winding tension, winding angle and also resin

content in every layer of the reinforcement. This is to guarantee fancied thickness and

quality of the composite are accomplished. The properties of the completed composite

can be shifted by the sort of winding pattern chosen. Besides that, there are three

fundamental fiber winding patterns, they are hoop winding, helical winding and polar

winding. However, in this project, helical winding has been chosen as the desired type of

winding as it is the most common one used in piping and vessels among the three. There

are a few reasons why the filament winding technique has been chosen as the desired

technique over others. The main one being that this technique can give an optimal

balance between hoop strength, tensile strength and torsion resistance. When combined

with a high fiber tension when applying the filaments, it results in a comparatively thin

walled product. On top of that, the epoxy resin or carbon fiber proportions are controlled

through computers. By this way, human error can be avoided and it will lead to less

variation in wall thickness in the end products. On top of that, this technique also

provides consistent product quality due to the highly automated nature of the process

[17].

12

It is important to find the optimum winding angle for filament winding. Several efforts

have been done to achieve this purpose. Based on previous studies, netting analysis is

one of the attempts to optimize composite tubular structures. This technique assumes

that fibers supported all loads, neglecting the contribution of the matrix and the

interaction between the fibers. The optimum angle obtained from this technique which is

57° is normally used to manufacture composite tubular structures under close-end

loading condition [19]. Optimum winding angle can be estimated by using ultimate

tensile strength along with applying netting analysis respect to 2:1 hoop-to-axial stress

ratio as it is shown at Equations (2) and (3), as illustrated in the figure below. The body

diagram of the cylinder consists of axial and hoop forces wrapped with the fibers at the

angle of “α” is indicated in the Figure 2.1 [20].

𝑁𝜃 = 𝜎𝑢𝑡 𝑠𝑖𝑛2𝛼 , 𝑁∅ = 𝜎𝑢𝑡 𝑐𝑜𝑠2𝛼 (2)

𝑁𝜃

𝑁∅= 𝑡𝑎𝑛2𝛼 = 2 → 𝛼 = 𝑎𝑟𝑐 tan (√2) = 𝟓𝟕° (3)

FIGURE 2.1: Body Diagram of Axial and Hoop Forces and Internal Pressure

13

2.6 Tensile Test

Tensile testing is utilized to measure the force needed to break a polymer composite

sample and the degree to which the sample stretches out or extends as far as possible.

The data is routinely used to demonstrate a material, to diagram parts to withstand

application power and as a quality control check of materials. Since the physical

properties of various materials can contrast dependent upon surrounding temperature, it

arrives and there suitable to test materials at temperatures that reproduce the normal end

use environment [21]. Tensile tests will be performed to measure the tensile properties

like tensile strength, tensile modulus and elongation at break. The tensile tests will be

measured by using a universal testing machine model AI-7000 M (Figure 2.2) according

to ASTM D638.

FIGURE 2.2: AI-7000 M Universal Testing Machine [21]

14

The mechanical property for tensile is tensile modulus. Solid body distorts when a

heap is connected to it. In case of when the material is elastic, the body returns to its

unique shape after the heap is removed. The material is straight if the proportion of

burden to deformation stays steady in the midst of the loading process. Very few

materials are straight and flexible past a little measure of deformation. A steady Young's

modulus applies to just straight flexible materials. A perfect inflexible material has an

endless Young's modulus in light of the fact that an interminable power is expected to

distort such a material. A material whose Young's modulus is high can be approximated

as unbending [21].

Tensile tests create a stress strain graph, which is utilized to decide tensile modulus.

ASTM D638 testing covers the determination of the in-plane tensile properties of

polymer matrix composite materials reinforced by high-modulus strands. The composite

material structures are limited to continuous fiber or discontinuous fiber-reinforced

composites in which the laminate is balanced and symmetric as for the test course. This

test decides in-plane tensile properties of polymer network composite (PMC) materials

reinforced by high-modulus strands. Composite material structures are restricted to

continuous fiber or discontinuous fiber reinforced composites where the laminate is

adjusted and symmetric concerning the test direction. A tensile sample is mounted in the

grasps of the testing machine. More often than not, load deformation or load strain

curves are plotted or digitally accumulated amid the test for the determination of the

elastic modulus [22].

15

2.7 Compression Test

Technically, compression test is an extremely useful way for large strain hardening

response of metals. Besides that, it is also convenient to prepare the specimens to

undergo testing. A length of pipe is placed in compression test machine and is subjected

to an increasing compressive load until failure occurs. The length change of the

specimen and the corresponding load is recorded at set intervals during the test. Strain

gauges may be attached to the test specimen to measure dimensional changes in the axial

directions. Compressive stress and strain are calculated and plotted as a stress-strain

diagram which will then be used when finding the elastic limit, proportional limit, yield

point, yield strength and compressive strength.

FIGURE 2.3: Universal Tensile Machine for Compression Test

16

According to the research of “A study on crushing behaviors of composite circular

tubes with different reinforcing fibers” by Jung-Seok Kim, Hyuk-Jin Yoon, Kwang-Bok

Shin [23], seven different kinds of circular tubes distinctly UD carbon/epoxy, UD

Kevlar/epoxy, UD carbon-Kevlar/epoxy, UD Kevlar-carbon/epoxy, PW carbon/epoxy,

PW Kevlar/epoxy and PW carbon-Kevlar/epoxy were fabricated. Compression tests

were carried out using a 100kN capacity hydraulic loading machine. All tubes were

compressed until the load increased fast by piling of debris inside them at loading rate of

10mm/min. During the tests, the load-displacement data was recorded as a function of

time at intervals of 0.1s. Five replicated tests were carried out [23].

FIGURE 2.4: Peak Loads of Past Research Samples

17

2.8 Microstructure Test

Scanning Electron Microscope (SEM) is used to examine microstructure of the carbon

fiber reinforced polymers (CFRP) samples and the formation of voids using different

arrangement of fiber tow (fiber tow of same size and different size). The examination of

the microstructure is done using a SEM model Phenom World Pro X that produces

images of a sample by scanning it with a focused beam of electrons. SEM can give

information about the sample’s surface topography and composition.

FIGURE 2.5: Scanning Electron Microscope (SEM)

18

2.9 CRFP in Oil & Gas Application

Carbon-fiber-reinforced polymer (CFRP) has become a prominent choice in

applications. The advantages of CFRP over steel as a pre-stressing material are namely

lightweight and corrosion resistance. These characteristics should enable the material to

be used for offshore environments. A research on Reinforced Composite Piping

Technology found that fiber-reinforced polymer are better than steel in terms of the

weight, to have the ability to withstand high internal pressures, good corrosion

resistance, impact resistance and torsion stiffness, lower life cycle cost, have smooth

surface and better dimensional stability over temperature fluctuations [24]. It is proved

that FRPs are better in terms of corrosion resistance as compared to steel where an

experience from an oil company’s used FRP pipes in low pressure water injection

networks at offshore installations outside the coast of Africa finds that there are no signs

of corrosion detected with Glass FRP pipes 12 after 2 years whereas the first holes were

observed after approximately 6 months with carbon steel [25].

Carbon fiber reinforced composite (CFRP) is also found to be ideally suitable material

for deep ocean applications. CFRP specimens when exposed at four depths namely 500,

1200, 3500, 4800 and 5100 m depths for 174 days did not lost in weight from weight

loss measurement [26]. Ultimate tensile strength from tensile test result for exposed

specimens is compared with controlled specimens. Tensile modulus data showed no

significant variation in property compared to control specimens. Compressive strength

of exposed specimens was also compared with control specimens. All the facts clearly

proved that deep-sea environment cannot affect the fiber/matrix interface. CFRP had not

undergone any change in property even after exposure in deepwater with temperature

test as high as 150°C. It can be concluded that carbon fiber reinforced composite is a

suitable material for deepwater applications through all the observation results obtained.

19

CHAPTER 3

METHODOLOGY

3.1 Research Methodology

In this project, the focal point lies on the behavior the carbon fiber wind to HDPE pipe

(CFWHP) gives when different types of carbon fiber tow arrangements are used when

forming the CFWHP. This final year project (FYP) has been divided into two major

parts, they are FYP I and FYP II. As mentioned earlier, a number of tasks needs to be

carried out before the final results of the research can be obtained. Hence, the tasks has

been divided accordingly between FYP I and FYP II.

FYP I

Preliminary research on carbon fiber wind to HDPE pipe (CFWHP)

Study the effect of different arrangements of carbon fiber tow on the mechanical

properties of CFWHP

Perform microstructure test using SEM machine using different carbon fiber tow

arrangements

Analyze and conclude the results obtained from the microstructure test

FYP II

Perform tensile test and compression test on CFWHP

Analyse and discuss the behavior of CFWHP under the conducted tests

20

3.2 Process Flow Chart

FIGURE 3.1: Project Process Flow Chart

Start

Literature review based on defined problem

Study the effect of physical arrangement of carbon fiber on the

mechanical properties of CFWHP

Conduct microstructure test using Scanning Electron Microscope

(SEM) to investigate on the void formation with different carbon

fiber tow arrangements

Preparation of CFWHP specimen for testing

Carry out tensile test and compression test and respectively

Conclusion

End

Study the behavior

of CFWHP under

conducted tests

21

3.3 Fabrication of CFWHP

In this project, 3 samples of carbon fiber wind to HDPE pipe (CFWHP) were

fabricated. Both of the samples are having 57° as the winding angle and 6 layers as the

winding thickness. 3 HDPE pipes with length of 2 meter each were used for each sample

respectively. CFWHP were produced by using 3-spindle, 4-axis filament winding

machine in SIRIM Permatang Pauh.

The process of fabricating the carbon fiber reinforces plastics is as below:

1) The mandrel consisting of HDPE pipe (Figure 3.2) is attached to the machine.

FIGURE 3.2: Liner for Winding

2) Four 12k (Sample A) fiber tows of carbon fibers are passed through the resin

bath (Figure 3.3) consists of epoxy. As it rotates, the roller comes in contact with

the fibers, so that the fibers are coated with the resin.

FIGURE 3.3: Resin Bath

22

3) The fibers coated with epoxy are wound around the mandrel (Figure 3.4).

4) The fibers move in lateral movement while the mandrel rotates with constant

speed. Several lateral movements are made to achieve the 6 layers thickness.

FIGURE 3.4: The Fibers Wounding the Mandrel

5) The fiber tows are cut when the sample finished. The mandrel rotates for a few

hours until the sample has hardened.

6) The sample was removed from the mandrel and placed in an oven (60 °C) in

duration of 3 hours for curing.

7) Steps 2 to 6 are repeated using two 12k and four 6k (Sample B) fiber tows and

eight 6k (Sample C) fiber tows.

23

3.4 Microstructure Test

SEM is used to examine microstructure of the carbon fiber reinforced polymers

(CFRP) samples and the formation of voids using different arrangement of fiber tow

(fiber tow of same size and different size). The examination of the microstructure is

done using a SEM model Phenom World Pro X that produces images of a sample by

scanning it with a focused beam of electrons. SEM can give information about the

sample’s surface topography and composition.

FIGURE 3.5: Scanning Electron Microscope (SEM)

TABLE 3.1: Technical Specifications of Scanning Electron Microscope (SEM)

Specifications

Light optical magnification 20 - 135x

Electron optical magnification range 80 - 100,000x

Resolution < 17 nm

Digital zoom Max 12x

High voltages Adjustable range between 4,8 kV and 15

kV imaging and analysis mode

Sample Size Up to 32 mm (Ø)

Sample Height Up to 100 mm

24

3.4.1 Sample Preparation

3.4.1.1 Sectioning & Cutting

The first step in preparing a specimen to analyse the microstructure is to locate the

area of interest. Cutting and sectioning is the most common technique to obtain the area

of interest. Proper cutting will produce flat and cut close to the area of interest and

minimal damage. In this project, the area of interest is the area where the group of fiber

tows intersects, as shown in Figure 3.2. At this area is where the no-fiber triangles

expected to be seen. After the area of interest is determined and marked, the CFRP is cut

into smaller specimens as shown in Figure 3.8.

FIGURE 3.6: The Cutting Area of the CFRP

25

FIGURE 3.7: Samples before Cutting

FIGURE 3.8: Samples after Cutting

26

3.4.1.2 Grinding & Polishing

Grinding process was performed by using Grinder and Polisher machine model

Metaserv 250 (Figure 3.9). The samples were grinded with SiC paper with running

water. The SiC paper used ranged from the 240 grit to 1200 grit. The grinding process is

done from coarsest to finest grit paper. This is to eliminate the scratches from the

previous grinding stage.

FIGURE 3.9: Metaserv 250

The grinding process is as follows:

1) SiC paper is placed on the grinding place, as shown in Figure 3.10, starting from

240 grit size. Water line is opened.

FIGURE 3.10: Placing of SiC Paper

27

2) The machine is switched on and the specimen is placed on the grinder, with the

surface to be examined faced down (Figure 3.11).

FIGURE 3.11: Grinding of the Specimen

3) Grind for 1 to 2 minutes.

4) Steps 1 to 3 are repeated using different grit paper; 320, 400, 600, 800, 1200 grit

size.

5) Close water line.

6) Specimen is then polished for around 1 to 2 minutes.

FIGURE 3.12: Polishing of the Specimen

28

3.4.1.3 Microstructure Test Procedure

The microstructure test is done based on the procedures as follows:

1) The sample is placed in the holder (Figure 3.13).

FIGURE 3.13: Placement of the Sample in the Holder

2) The holder height is adjusted (Figure 3.14).

FIGURE 3.14: Adjustment of the Holder Height

29

3) The holder is placed in the Phenom (Figure 3.15).

FIGURE 3.15: Placement of the Holder in the Phenom

4) The microstructure is observed from the desktop. The resolution can be adjusted

accordingly.

FIGURE 3.16: Observation of the Microstructure

30

3.5 Tensile Test (ASTM D638)

Tensile tests will be performed to measure the tensile properties like tensile strength,

tensile modulus and elongation at break. The tensile tests will be measured by using a

universal testing machine model AI-7000 M (Figure 3.17) according to ASTM D638.

Table 3.2 shows the technical specifications of the machine [18].

FIGURE 3.17: AI-7000 M Universal Testing Machine [18]

TABLE 3.2: Technical Specifications of Universal Testing Machine [18]

Specification

Capacity 1020 Kn

Load Resolution 1/200,000 (or 1/300,00 specified by user)

Stroke (exclude the grips) 1100 mm

Effective width 410 mm

Test Speed 0.001~1000 mm/min or 0.001~1500

mm/min

Sample Rate 1000 times/sec

Motor AC Servo Motor

Power 1∮, 220V, 15A , 50Hz/60Hz or specified

by user

31

The procedures of tensile test based on ASTM D638 are as follows:

1) 3 pieces of dog-bone shape specimens (Figure 3.18) are prepared according to

ASTM D638 Standard.

2) Specimens are subjected to pulling speed of 20mm/min until failure.

3) Experiment are repeated 3 times to increase accuracy of results.

4) Stress-strain curve is then plotted and study the results to determine modulus of

elasticity and maximum tension to failure.

FIGURE 3.18: Dog-Bone Specimen Shape for Tensile Test (ASTM D638)

32

3.6 Compression Test (ASTM D695)

The procedures for compression test are as follows:

1) 3 pieces of 100mm CFWHP specimens are prepared according to ASTM D695

standard.

2) The specimen is placed in axial position (Figure 3.19).

3) Specimens are subjected to compression speed of 20mm/min until failure.

4) Experiment are repeated 3 times to increase accuracy of results.

5) Load-displacement curve is then plotted and study the results to determine energy

absorption and maximum load to failure.

After obtaining load-displacement curves of all specimens, the maximum loads,

mean loads and energy absorption values were calculated and reported for each

test group.

FIGURE 3.19: CFWHP Pipe Specimen in Axial Position Compression Test

33

3.7 Gantt Chart & Key Milestones

FYP I

Planning Key Milestones

The Gantt chart above shows the research activities and key milestones that would be conducted in Final Year Project I.

No. Detail/Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 Selection of Project Title

2 Preliminary research on carbon fiber

wind to HDPE pipe (CFWHP)

3 Study the effect of different

arrangements of carbon fiber tow on the

mechanical properties of CFWHP

4 Submission of Extended Proposal

5 Detailed Research Work

6 Proposal Defence

7 Perform microstructure test using SEM

machine and analyse the results obtained

8 Interim Draft Report Submission

9 Interim Report Submission

34

FYP II

Planning Key Milestones

The Gantt chart above shows the research activities and key milestones that would be conducted in Final Year Project II.

No. Detail/Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 Fabrication of CFWHP samples

2 Sample preparation for tensile test and

compression test

3 Perform tensile test, and analyse the

results obtained

4 Submission of Progress Report

5 Perform compression test and analyse

the results obtained

6 Pre-Sedex

7 Submission of Draft Final Report

8 Submission of Dissertation (Soft Bound)

9 Submission of Technical Paper

10 Viva

11 Submission of Dissertation (Hard Bound)

35

CHAPTER 4

RESULTS & DISCUSSION

4.1 Microstructure Test Analysis (Surface Section)

Calculations for samples A1 (12k), B1 (12k + 6k) & C1 (6k)

Table 4.1 shows the calculations that have been obtained from the microstructure test for

all the three samples for surface section. These calculations have been calculated using

Equation (5).

TABLE 4.1: Calculations for 12k samples

Sample Sample Height (m) Base (m) Area (m2)

A1

0.003

3 X 0.000474

4.266E-06

B1

0.003

5 X 0.000211

3.165E-06

C1

0.003

7 X 0.000098

2.058E-06

Figure 4.1 shows the point of interest of the sample that underwent the microstructure

test for surface section.

Formula to calculate area of void (surface section)

Area of void (m2) = Base length (m) X Height of sample (m) (5)

Assumptions:-

Base (m) = x

For A1 = 3x

For B1 = 5x

For C1 = 7x FIGURE 4.1: Surface Section Point of Interest

Point of Interest

36

Figure 4.2, 4.3, and 4.4 illustrates the hypothesis of carbon the carbon fiber tow

arrangement. X represents the length of void area.

FIGURE 4.2: 12k Fiber Tow Sample Arrangement

FIGURE 4.3: 12k + 6k Fiber Tow Sample Arrangement

FIGURE 4.4: 6k Fiber Tow Sample Arrangement

X X X

X X X X X

X X X X X X X

37

FIGURE 4.5: Comparison of Void Areas (Surface Section) using Different Fiber Tow

Arrangements

The comparison chart above (Figure 4.5) justifies that the area of voids for surface

section for 6k fiber tow sample is the smallest when compared with the 12k fiber tow

sample and the 12k + 6k fiber tow sample. Table 4.1 shows the mathematical proof to

support that statement. This shows that the increment of fiber content lead to the

decrease in the area of voids. Furthermore, during the fabrication of the samples, the

bandwidth of both types of sample are maintained the same. This leads to the increase in

space between each tow of the CFWHP samples.

4.27E-06

3.17E-06

2.06E-06

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

3.00E-06

3.50E-06

4.00E-06

4.50E-06

VO

ID A

REA

(M

2 )

FIBER TOW ARRANGEMENTS

Void Area Comparison

12k 12k+6k 6k

38

Sample using 12k fiber tow arrangements

FIGURE 4.6: Surface Void Formation for Sample A1

Figure 4.6 above shows the SEM results obtained from the microstructure test for the

12k sample.

39

Sample using 12k + 6k fiber tow arrangements

FIGURE 4.7: Surface Void Formation for Sample B1


12k + 6k sample

40

Sample using 6k fiber tow arrangements

FIGURE 4.8: Surface Void Formation for Sample C1

Figure 4.8 above shows the SEM results obtained from the microstructure test for the 6k

sample.

41

4.2 Microstructure Test Analysis (Cross Section)

Table 4.2, 4.3 and 4.4 shows the result obtained from the microstructure test for all the

three samples for cross section. The calculations have been calculated using Equation

(6).

Calculations for samples A1 & A2 (12k)


Sample Average Height (m) Base (m) Area (m2)

A1

0.000029550

0.000369000

1.0904E-08

A2

0.000043075

0.000231000

9.9503E-09

Average

1.0427E-08

Calculations for samples B1 & B2 (12k + 6k)



B1

0.000022150

0.000276000

6.1134E-09

B2

0.000026750

0.000474000

1.2680E-08

Average

9.3965E-09

42

Calculations for samples C1 & C2 (6k)



C1

0.000027175

0.000432000

1.17396E-08

C2

0.000022400

0.000275000

6.1600E-09

Average

8.9498E-09

Formula to calculate area of void (cross section)

Area of void (m2) = Average height (m) X Base length (m) (6)

FIGURE 4.9: Cross Section Point of Interest

Figure 4.9 shows the point of interest of the sample that underwent microstructure test

for cross section.

Point of Interest

43

FIGURE 4.10: Comparison of Void Areas (Cross Section) using Different Fiber Tow

Arrangements

The comparison chart above (Figure 4.10) justifies that the area of voids for cross

section of 6k fiber tow sample is the smallest when compared with the 12k fiber tow

sample and the 12k + 6k fiber tow sample. Table 4.2, 4.3 and 4.5 shows the

mathematical proof to support that statement. This shows that the increment of fiber

content lead to the decrease in the area of voids. Furthermore, during the fabrication of

the samples, the bandwidth of both types of sample are maintained the same. This leads

to the increase in space between each tow of the CFWHP samples.

1.04E-08

9.40E-09

8.95E-09

8.00E-09

8.50E-09

9.00E-09

9.50E-09

1.00E-08

1.05E-08

1.10E-08V

OID

AR

EA (

M 2

)


Void Area Comparison

12k 12k+6k 6k

44

Samples using 12k fiber tow arrangements

The samples have been labelled as A1 respectively.

FIGURE 4.11: Cross Section Void Formation for Sample A1


12k sample.

45

Samples using 12k + 6k fiber tow arrangements

The samples have been labelled as B2.

FIGURE 4.12: Cross Section Void Formation for Sample B2


12k +6k sample.

46

Samples using 6k fiber tow arrangements

The samples have been labelled as C2.

FIGURE 4.13: Cross Section Void Formation for Sample C2


6k sample.

47

4.3 Tensile Test (ASTM D638)

TABLE 4.5: Tensile Test Result Tabulation

Sample Failure Mode Original

Length

Average

Final

Length

Average

Max. Load

Tensile

Stress

12k

(A1, A2 &

A3)

Very brittle for carbon

fiber layer, surface of

failure is even without

much resistance

towards the pulling

force

115mm

120mm

1,127.67 N

7.81 MPa

12k + 6k

(B1, B2 &

B3)

Slightly brittle for

carbon fiber layer,

surface of failure is

not so even with slight

resistance towards the

pulling force

115mm

120mm

1,383.67 N

10.07 MPa

6k

(C1, C2 &

C3)

Brittle for carbon fiber

layer, surface of

failure is not even with

resistance towards the

pulling force

115mm

121mm

1,891.33 N

12.66 MPa

The table above (Table 4.5) tabulates the results obtained from the tensile test

conducted. 3 samples were tested for each different carbon fiber tow arrangement. From

the obtained results, an average reading has been calculated for all the 3 different fiber

tow arrangements. Samples A which are the 12k samples displays an even surface

breakage while the B samples which are the 12k + 6k samples shows a slightly uneven

surface breakage. However, the C samples which are the 6k samples shows a very

uneven surface breakage. This is due to the stronger 6k samples’ ability to resist the

pulling more efficiently when compared to the 12k + 6k samples (B) and also the 12k

samples (A).

48

FIGURE 4.14: Comparison of Tensile Test Stress Loads using Different Fiber Tow

Arrangements

The chart above (Figure 4.14) clearly shows the tensile stresses for all the 3 samples.

The strongest sample being the 6k sample (C), followed by the 12k + 6k sample (B) and

finally the 12k sample (A). This further proves the theory of where the void area plays a

role in the strength of the material. Smaller void areas results in a stronger material.

Based on the results obtained from the microstructure test, the 6k samples (C) had the

smallest void area followed by the 12k + 6k sample (B) and finally the 12k sample (A).

The figures below shows the stress-strain curve of all the samples involved in the tensile

test. The results clearly shows that the 6k samples (C) require higher stress value in

order to reach its failure point when compared to the 12k + 6k samples (B) and the 12k

samples (A). Below are images of the sample after undergoing tensile tests.

7.810

10.07

12.66

0.000

2.000

4.000

6.000

8.000

10.000

12.000

14.000ST

RES

S (M

PA

)


Tensile Test Stress

12k 12k+6k 6k

49

FIGURE 4.15: Stress-Strain Curve for Sample A (12k)

Due to certain machine limitations, the graphs obtained from tensile test are not as

expected. To get better and more accurate results, better machines are recommended to

be used in the future.

50

FIGURE 4.16: Stress-Strain Curve for Sample B (12k + 6k)




51

FIGURE 4.17: Stress-Strain Curve for Sample C (6k)




52

FIGURE 4.18: Samples A (12k) after Tensile Test

FIGURE 4.19: Samples B (12k + 6k) after Tensile Test

FIGURE 4.20: Samples C (6k) after Tensile Test

Figure 4.18, 4.19 and 4.20 shows the three samples after undergoing tensile test. As we

can see, the matrix fails first and later on followed by the carbon fiber reinforcement.

Hence, the failure modes are achieved as the figure above.

53

4.4 Compression Test (ASTM D695)

Table 4.6 shows the result obtained from the compression test for all three samples. The

calculations have been calculated using Equation (7) and Equation (8).

TABLE 4.6 : Compression Test Result Tabulation

Sample Original

Length

Average

Final

Length

Average

Max. Load

Average

Mean

Load

Energy

Absorption

Specific

Energy

Absorption

12k

(A1, A2

& A3)

100mm

60mm

95.60 kN

57.10 kN

2.28 kNm

10.20 J/kg

12k +

6k

(B1, B2

& B3)

100mm

60mm

106.55 kN

68.48 kN

2.74 kNm

12.23 J/kg

6k

(C1, C2

& C3)

100mm

60mm

117.48 kN

79.42 kN

3.18 kNm

14.18 J/kg

Formula to calculate Energy Absorption

Energy Absorption (J/kg) = Average Mean Load (kN) X (Df – Di) (m) (7)

Formula to calculate Specific Energy Absorption

Specific Energy Absorption (kN) = Energy Absorption (kNm) ÷ Mass (g) (8)

54

Stage 1 Stage 2 Stage 3 Stage 4

Stage 1

Both ends of sample start to experience axial compression force. It starts to transfer the

load force from both ends towards the center part of the sample.

Stage 2

Compression force at both ends of the sample reached maximum and eventually the

center part of the sample starts to experience deformation. “Crack” sound starts to

appear as it signifies the breaking of the outer layer of carbon fiber.

Stage 3

“Crack” sound frequency increases to show that more and more fibers are breaking at

the outer layer. Load force starts to be transferred from outer layer of carbon fiber

towards inner layer of HDPE pipe.

Stage 4

At this final stage, the outer layer of carbon fiber experience cracks and defragmentation

until it eventually fails. HDPE pipe at the inner layer continues to experience the load

force until eventually deforming and exceeding its elastic limits.

55

FIGURE 4.21: Compression Test Load-Displacement Curve

Figure 4.21 shows the load-displacement curve of 12k sample (A) versus 12k+6k sample

(B) and 6k sample (C) in compression test. Result clearly shows that 6k sample has

larger area under the curve profile as compared to 12k+6k sample and 12k sample which

contributed to higher energy absorption value as recorded in table 4.6. The graph also

shows that 6k sample can tolerate with much higher load before it eventually fails as

compared to 12k+6k sample. This further proves the theory of the smaller void area

sample having the highest strength, as found in the microstructure test, the 6k sample

has the smallest void area. Below are images of the samples after undergoing the

compression test.

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70

LOA

D (

kN)

DISPLACEMENT (mm)

Load-Displacement Curve

A

B

C

56

Figure 4.22 and 4.23 shows the 12k samples after undergoing compression test. As can

be observed, the samples undergo folding of two lobes in order to defend the HDPE

layer inside.

FIGURE 4.22: Side View of Samples A after Compression Test

FIGURE 4.23: Top View of Samples A after Compression Test

57

Figure 4.24 and 4.25 shows the 12k + 6k samples after undergoing compression test. As

can be observed, the sample undergoes folding of 2 lobes in order to defend the HDPE

layer inside.

FIGURE 4.24: Side View of Samples B after Compression Test

FIGURE 4.25: Top View of Samples B after Compression Test

58

Figure 4.26 and 4.27 shows the 6k samples after undergoing compression test. As can be

observed, the sample undergoes folding and fragmentation. In order to defend the HDPE

the carbon fiber undergoes folding, once the carbon fiber can no longer sustain the force,

the HDPE layer inside starts to expand which causes the carbon fiber to undergo

fragmentation. This explains the high energy absorptions values for the 6k samples.

FIGURE 4.26: Side View of Samples C after Compression Test

FIGURE 4.27: Top View of Samples C after Compression Test

0 35 70 mm

59

CHAPTER 5

CONCLUSION & RECOMMENDATIONS

5.1 Conclusion

The first objective of this project was to study how various sizes of carbon fiber tow

arrangements affect the level of enhancement of mechanical properties the carbon fiber

wind to HDPE pipe (CFWHP). Microstructure test analysis showed that the void area of

6k (Samples C) CFRP is smaller than the void areas of the 12k (Samples A) CFRP and

the 12k + 6k (Samples B) CFRP. This is due to the higher fiber content in the 6k CFRP.

Hence it is observed that the different arrangements of fiber tow with the maintained

number of tows and bandwidth size does cause changes in the formation of voids.

From the tensile test, it has been concluded that the strongest sample is the 6k sample

(C), followed by the 12k + 6k sample (B) and finally the 12k sample (A). This further

proves the theory of where the void area plays a role in the strength of the material.

Smaller void areas results in a stronger material. Based on the results obtained from the

microstructure test, the 6k samples (C) had the smallest void area followed by the 12k +

6k sample (B) and finally the 12k sample (A). As for the stress-strain curve obtained of

all the samples involved in the tensile test, the results clearly shows that the 6k samples

(C) require higher stress value in order to reach its failure point when compared to the

12k + 6k samples (B) and the 12k samples (A).

As for the compression test, the load-displacement curve of 12k sample (A) versus

12k+6k sample (B) and 6k sample (C) in compression test. Result clearly shows that 6k

sample has larger area under the curve profile as compared to 12k+6k sample and 12k

sample which contributed to higher energy absorption value as recorded in table 4.6. The

graph also shows that 6k sample can tolerate with much higher load before it eventually

fails as compared to 12k+6k sample. This further proves the theory of the smaller void

area sample having the highest strength, as found in the microstructure test, the 6k

sample has the smallest void area.

60

In a nutshell, the parties involved in the oil and gas industry are now looking into other

alternatives when it comes to pipelines. This is because, the existing commercial

metallic pipelines are very much prone to corrosion. So, the solution that has been

proposed is to bring in non-metallic pipelines into play. To be precise, composite

material pipelines. The composite material chosen for this solution is carbon fiber

reinforced polymer (CFRP). Non- metallic pipelines are corrosion resistant and also

have a lifespan of around 50 years or so. Tests has been done in order to show that the

usage of non-metallic pipelines brings in far more advantages than the commercial steel

pipelines.

5.2 Recommendation

Further research with CFRP with less than 6 fiber tows with different size of fiber

tows to fill in the no-fiber triangle as compared to the 12k, 12k + 6k, and 6k fiber tow

samples after analyzing the results obtained from the microstructure test and also the

tensile test. For instance, 3k carbon fiber tow samples maybe used. A sample which has

16 fiber tows of 3k carbon fiber and a sample of 8 fiber tows of 3k carbon fiber and 4

fiber tows of 6k carbon fiber can be put through testing to study even further the effect

of different carbon fiber tow arrangements has on the mechanical properties of CFWHP.

Besides that, better machines could be used for the microstructure test. The current SEM

machine used for this project has its limitations when measuring the length of void.

Some of the voids proved to be too long for the machine to measure. Hence, a better

machine may prove to provide a more accurate result.

61

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64

APPENDICES

Tensile Test Sample 12k

66

Tensile Test Sample 12k+6k

68

Tensile Test Sample 6k

70

Compression Test All Samples Summary

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70

LOA

D (

kN)

DISPLACEMENT (mm)

Load-Displacement Curve

A

B

C

n a study of mechanical properties and crushing

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